The present invention relates generally to sandwich constructions suitable for use in structural and non-structural members, and more particularly to sandwich constructions of low-density cores secured between thin-gauge, high-strength face sheets for use in a wide range of military, industrial and commercial components.
Sandwich constructions are finding broad application as structural and non-structural members in boats, aircraft, furniture, refrigerators, and other items requiring high strength, lightweight materials. They typically include face sheets bonded to either side of a low density core. The sheets are made of such materials as metals, plastic, or composite fiber glass laminates for rigidity and strength. Among the various core materials, are rigid plastic foams and honeycombs made from layers of corrugated metal sheets or expanded layers of resin-impregnated plastic sheets.
In airplane design the need for weight efficiency and aerodynamically smooth surfaces under high stress levels has stimulated use of sandwich construction as a possible substitute for the conventional sheet-stringer construction. Notwithstanding the superior weight-efficiency of the sandwich constructions, their general acceptance for critical applications has lagged behind theoretical development primarily because of maintenance problems experienced in service. Honeycomb core sandwich constructions are considered to be among the most weight-efficient but, they have a tendency to retain moisture which may become entrapped due to ineffective edge seals, damage to the face sheets or unbonding of face sheets from the core. This may degrade the structural integrity and lead to extensive corrosion and premature failure of components. Experience has shown a significant frequency of repairs on sandwich structures or sandwich structure part replacements which are very time-consuming and expensive.